The present invention relates to magnetic disc drives. More particularly, the present invention relates to correction of errors in header information in a magnetic disc drive.
Magnetic recording devices are used to magnetically store information. Typically, the entire magnetic storage medium is not used to record the user "data." A portion of the information carried on the medium is called a "header" and carries information related to the data, which (on most formats) follows the header. The header includes an LBA (logical block address) which is an address used to identify, i.e ID, the location of the data. The header also contains flags and skip descriptors for microdefect or servoburst skips (typically two bytes per skip descriptor).
The prior art has been directed to detection rather than correction of header errors. Upon detection, the disc controller must abort the data read and wait for the header data to come around a second time for a retry. This is time consuming and negatively impacts system performance.
The time period incurred between the reading of a header and the following data field as the disc spins translates into a physical gap. This gap is wasted space on the storage medium. The more processing that the disc controller must do during this period, the longer the period and the gap. Typical error correction techniques for the data field are complex and time consuming, requiring many "byte times" to process the information which can be on the order of a full sector readback time; even for "on-the-fly" techniques. Thus, typical error correction techniques are not appropriate because of the time required to correct the error(s) before comparison between the corrected header LBA and target or searched LBA can be made, allowing for the decision of whether the subsequent associated data field should be read or written. Even a small delay will cause a significant reduction in disc storage capabilities because each header on the disc will require a longer gap preceding the data field.
Techniques are known for correcting errors occurring in the data field. For example, U.S. R. No. RE34,088 reissued Oct. 6, 1992 entitled ON THE FLY ERROR CORRECTION shows an apparatus for correcting errors in data fields. However, these techniques are not appropriate for header information due to the aforementioned gap.